1. Technical Field
The present specification describes a step-down switching regulator, and more particularly, a step-down switching regulator formed by integrating a high-voltage MOS transistor and a low-voltage MOS transistor in a single semiconductor chip.
2. Discussion of the Background
Switching regulators are electrical circuits for stabilizing an output voltage by high-speed on-off operation. When an input voltage is high, conventional switching regulators use high-voltage transistors for withstanding a voltage higher than the input voltage. However, the high-voltage transistors are larger in size, drive a smaller amount of current, and have a slower response speed than low-voltage transistors do.
Such switching regulators include a switching element in which a largest amount of current flows. By using a NMOS (negative channel metal oxide semiconductor) transistor rather than a PMOS transistor (positive channel metal oxide semiconductor), the switching element can achieve high efficiency in flowing a large amount of electrical current at a high speed.
However, in a case of a step-down switching regulator, when a NMOS transistor is used for the switching element, a drain of which is directly connected to an input voltage, since a source voltage increases up to about the input voltage when the NMOS transistor is turned on, a gate voltage for turning on the NMOS transistor needs to be greater than the input voltage.
To address this problem, a related-art switching regulator includes a bootstrap capacitor. The bootstrap capacitor generates a voltage greater than an input voltage to turn on and off the NMOS transistor switching element with the generated voltage.
However, even though the switching element uses the NMOS transistor, use of high-voltage transistors for all transistors included in the switching regulator results in an increase in chip area and a decrease in response speed.
Accordingly, there is a need for a technology to provide a step-down switching regulator capable of decreasing chip area and increasing response speed while withstanding high input voltage.